G. Cecconi

WIGWAM-Venice Resilience Lab

Introduction

During the last 20 years the 224 arches of the bridge connecting Venice with inland has been clogged by 2m reefs of oysters (Crassostrea gigas) till the elevation of mean high tide. This has produces stagnation of the water, siltation of the navigation channels, risk of anoxia and an excess of turbidity. All these factors are impeding the growth of bio structuring habitat. A bottom-up co-produced project with the reuse of oysters and dredged sediments for increasing tidal flushing in the open waters and the retention of pollution and sediments in the Osellino and Dese Delta has been developed and submitted to the EU LIFE-BIODIVERSITY 2018 Program for co-financing.

Methods

Using a hydrodynamic model, we have found the possibility of inducing a residual current across the bridge reopening only few arches together with tentative channels that we foresee will expand naturally under the tidal flow. Also, with a limited amount of dredging we have demonstrated the possibility of retaining nutrients and turbidity inside the delta of Dese and Osellino river increasing the depuration of water entering the open lagoon and increasing also the accretion capacity of the salt-marsh wetlands, with a greater increase of C=2 trapping and adaptation to sea level rise.

Results

Presentation of the dredging for tidal flushing and the delta retention works together with the simulation of their effects with a 2-D hydrodynamic model. The possibility to install a vegetated floating mattress for wave dumping and water depuration instead of oyster shoals will be discussed comparing the effects and costs of the two solutions.

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Figure 1 The retention structures at the Osellino Delta and the effects on water levels.

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